[C#]透過PerformanceCounter取得特定Process的CPU使用率

想要透過PerformanceCounter取得特定Process的CPU使用率，首先我們要理解這部分的資料在PerformanceCounter是怎樣分布的。這邊我們可以叫出效能監視器後，找到Process分類，可以看到如下畫面，所有的Process都有對應的Instance，像是chrome、chrome#1、chrome#11…。

所以我們的第一步就是要從Process找到對應的Process Instance Name。但是BCL內建的Process類別中並未有這樣的資訊，要怎樣找到呢？這邊可透過另一個名叫ID Process的PerformanceCounter輔助，對照筆者準備的兩張圖，不難發現該PerformanceCounter的值對應的就是Process的PID。

這給我們了一個提示，我們可透過這個這個PerformanceCounter反查到Process的Instance Name，像是下面這樣：

private string GetProcessInstanceName(int pid) { var category = new PerformanceCounterCategory(“Process”);

var instances = category.GetInstanceNames(); foreach (var instance in instances) {

using (var counter = new PerformanceCounter(category.CategoryName, “ID Process”, instance, true)) { int val = (int)counter.RawValue; if (val == pid) { return instance; } } } throw new ArgumentException(“Invalid pid!”); }

取得了Process的Instance Name後，CPU的使用率我們就可以透過另一個名為% Processor Time的PerformanceCounter下去取得，像是下面這樣：

private static int GetCpuUsage(int pid) { if (!m_CounterPool.ContainsKey(pid)) { m_CounterPool.Add(pid, new PerformanceCounter(“Process”, “% Processor Time”, GetProcessInstanceName(pid))); }

var lastUpdateTime = default(DateTime);

m_UpdateTimePool.TryGetValue(pid, out lastUpdateTime);

var interval = DateTime.Now - lastUpdateTime;

if (interval.TotalSeconds > 1) { m_CpuUsagePool[pid] = (int)(m_CounterPool[pid].NextValue() / Environment.ProcessorCount); }

return m_CpuUsagePool[pid]; }

這邊要特別注意的是，Query PerformanceCounter的時候，必須要間隔一秒，不然會一直Query到錯誤的值。還有就是取得的值必須要除以核心數才會是我們期望的值。

為了方便重用，依慣例筆者還是稍微整理了一下擴充方法：

using System; using System.Collections.Generic; using System.Diagnostics; using System.Linq; using System.Text; using System.Threading; using System.Threading.Tasks; using System.Windows.Forms;

public static class ProcessExtension { #region Private Static Var private static Dictionary _counterPool; private static Dictionary _updateTimePool; private static Dictionary _cpuUsagePool; #endregion

#region Private Static Property private static Dictionary m_CounterPool { get { return _counterPool ?? (_counterPool = new Dictionary()); } }

private static Dictionary m_UpdateTimePool { get { return _updateTimePool ?? (_updateTimePool = new Dictionary()); } }

private static Dictionary m_CpuUsagePool { get { return _cpuUsagePool ?? (_cpuUsagePool = new Dictionary()); } } #endregion

#region Private Static Method private static string GetProcessInstanceName(int pid) { var category = new PerformanceCounterCategory(“Process”);

var instances = category.GetInstanceNames(); foreach (var instance in instances) {

using (var counter = new PerformanceCounter(category.CategoryName, “ID Process”, instance, true)) { int val = (int)counter.RawValue; if (val == pid) { return instance; } } } throw new ArgumentException(“Invalid pid!”); }

private static int GetCpuUsage(int pid) { if (!m_CounterPool.ContainsKey(pid)) { m_CounterPool.Add(pid, new PerformanceCounter(“Process”, “% Processor Time”, GetProcessInstanceName(pid))); }

var lastUpdateTime = default(DateTime);

m_UpdateTimePool.TryGetValue(pid, out lastUpdateTime);

var interval = DateTime.Now - lastUpdateTime;

if (interval.TotalSeconds > 1) { m_CpuUsagePool[pid] = (int)(m_CounterPool[pid].NextValue() / Environment.ProcessorCount); }

return m_CpuUsagePool[pid]; } #endregion

#region Public Static Method public static string GetInstanceName(this Process process) { return GetProcessInstanceName(process.Id); }

public static int GetCpuUsage(this Process process) { return GetCpuUsage(process.Id); } #endregion }

已筆者的測試範例來說，撰寫起來會像下面這樣：

using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Diagnostics; using System.Drawing; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Windows.Forms;

namespace WindowsFormsApplication24 { public partial class Form1 : Form { public Form1() { InitializeComponent(); }

private void Form1_Load(object sender, EventArgs e) { timer1.Interval = 1000; lbxProcess.DisplayMember = “ProcessName”; lbxProcess.DataSource = Process.GetProcesses(); }

private void lbxProcess_SelectedIndexChanged(object sender, EventArgs e) { var selectedProcess = lbxProcess.SelectedItem as Process; if (selectedProcess == null) return;

timer1.Enabled = false; tbxInstanceName.Text = selectedProcess.GetInstanceName(); tbxCPU.Text = selectedProcess.GetCpuUsage().ToString(); timer1.Enabled = true; }

private void timer1_Tick(object sender, EventArgs e) { var selectedProcess = lbxProcess.SelectedItem as Process; if (selectedProcess == null) return;

tbxCPU.Text = selectedProcess.GetCpuUsage().ToString(); } } }

運行結果：